RU2348612C2 - Method of obtaining 21,4,41-trinitrobenzanilide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention concerns organic chemistry and method of obtaining 2¹,4,4¹-trinitrobenzanilide (TNBA), a semiproduct of 5(6)-amino-2-(4-aminophenyl)benzimidazol synthesis, applied as monomer in production of heat resistant and high-strength fibre. Method involves acylation of 2,4-dinitroaniline by 4-nitrobenzoilchloride taken in excess by over 5 mol % in relation to 2,4-dinitroaniline, at gradual temperature increase to boiling point at atmospheric pressure, in the presence of iron chloride as catalyst; separation of 2¹,4,4¹-trinitrobenzanilide by sequence of crystallisation, filtration and neutralisation by ammonium in water suspension. Mother solution formed after crystallisation and filtration is recycled at the next acylation stage, and neutralisation is performed at temperature under 60°C with dosed supply of aqueous ammonium solution.

EFFECT: efficient novel method of obtaining the compound.

6 cl, 6 ex, 1 dwg, 1 tbl

Description

The present invention relates to the field of organic chemistry and relates to a method for producing 2 ', 4,4'-trinitrobenzanilide, an intermediate in the synthesis of 5 (6) amino-2- (4-aminophenyl) benzimidazole, used as a monomer in the production of heat-resistant and high-strength fibers.

A known method of producing 2 ', 4,4'-trinitrobenzanilide (hereinafter TNBA) by nitration of N- (4'-nitrobenzoyl) aniline with nitric acid in a concentrated sulfuric acid medium (US Patent 4109093, NCI 548 / 310.7, publ. 08/22/1978 ) The main disadvantage of this method is the large amount of waste - a mixture of concentrated sulfuric and nitric acids contaminated with impurities of organic substances.

The closest analogue of the proposed method for producing TNBA (prototype) is a method based on the acylation of 2,4-dinitroaniline with 4-nitrobenzoic acid in the presence of an activator - polychlorocyclophosphazene and a catalyst - pyridine N-oxides or β- and γ-picoline in chlorobenzene medium, followed by isolation the target product by distillation of chlorobenzene with water vapor (AS USSR 1025093, C07C 233/66, publ. 02.20.1999). At a temperature of 130-133 ° C, the process ends within 1 hour, the yield of 2 ', 4,4'-trinitrobenzanilide is 93-96%. Polychlorocyclophosphazene, for example hexachlorocyclophosphazene, is synthesized from ammonium chloride and phosphorus pentachloride. In the known method, up to 0.7 g of hexachlorocyclophosphazene is used per 1.1 g of 2,4-dinitroaniline, so polychlorocyclophosphazene is actually a co-reagent. The process as a whole is accompanied by the formation of a large amount of hydrogen by-product; the problem of recycling phosphorus-containing production waste arises. Phosphorus pentachloride is extremely hygroscopic, toxic, and corrosive. Since phosphorus pentachloride is a crystalline product, working with it causes a number of problems in the hardware design of the process. The synthesis uses expensive inaccessible catalysts. Apparently, the acylation reaction proceeds through the stage of in situ formation of 4-nitrobenzoyl chloride from 4-nitrobenzoic acid and polychlorocyclophosphazene. For these reasons, the synthesis of TNBA by a known method did not find practical application. If phosphorus chlorides were used in the synthesis, it would be easier to obtain 4-nitrobenzoyl chloride by reacting 4-nitrobenzoic acid with phosphorus oxychloride.

Thus, the disadvantages of the method according to the prototype are the use of inaccessible and expensive activator and catalysts, their high consumption, the formation of a significant amount of production waste.

The objective of the present invention is to develop a method for producing TNBA, devoid of the disadvantages inherent in the prototype.

The problem is solved by the proposed method for the production of TNBA by acylation of 2,4-dinitroaniline (DND) with 4-nitrobenzoyl chloride (PNBH) in the presence of a catalyst when heated in an organic solvent.

The proposed method is characterized in that the acylation of 4-nitrobenzoyl chloride, taken in excess of more than 5 mol.% With respect to 2,4-dinitroaniline, is carried out with a gradual increase in temperature to a boil at atmospheric pressure, in the presence of ferric chloride as a catalyst, 2 ', 4,4'-trinitrobenzanilide is isolated by sequential crystallization, filtration and neutralization with ammonia in an aqueous suspension, the reaction mother liquor formed after crystallization and filtration is recycled to the next acylation operation. The recycling can be carried out an unlimited number of times, while the entire mother liquor or part of it can be returned to the recycling without any processing. If necessary, the mother liquor can be purified by treatment with an adsorbent, for example, activated carbon.

As an organic solvent in the process of producing TNBA, solvents can be used that form an azeotrope with water: chlorobenzene, p-xylene, o-xylene, technical mixture of xylenes, ethylbenzene or toluene.

The acylation reaction of 2,4-dinitroaniline (DND) with 4-nitrobenzoyl chloride (PNBH) in the presence of ferric chloride in an organic solvent proceeds at a noticeable rate, starting from a temperature of 65-85 ° С. With a further increase in temperature, the reaction rate increases and at 100-120 ° С the acylation process in the initial period proceeds intensively with the release of hydrogen chloride (see drawing). To prevent too intense evolution of hydrogen chloride and ejection of the reaction mass, the process is conducted with a gradual increase in temperature to boiling point at atmospheric pressure. For this purpose, it is also advisable to use a metered supply of PNBH to the reaction zone in solid form or in the form of a melt, or in the form of a solution in an appropriate solvent at a temperature at which the reaction proceeds at a high speed, for example, at the boiling point of the reaction mixture.

A preferred excess of PNBH with respect to DND is an excess of 10-15 mol%. With an excess of PNBH of less than 10 mol%, the TNBA yield decreases, and with an excess of more than 15 mol%, it is difficult to wash TNBA from excess PNBH.

To prevent the accumulation of excess solvent in the reaction mass, which comes with the recycled mother liquor, with a solution of PNBH in the corresponding solvent or with a solution, suspension or paste of DND, part of the solvent is distilled off directly from the acylation reactor during the reaction, combining the acylation and distillation of the solvent into time. As a result, there is no need to use additional equipment for solvent stripping.

It is advisable to neutralize TNBA in an aqueous suspension with ammonia to remove PNBH residues and NSC impurities under milder conditions than in the prototype, namely at 20-60 ° C with a gradual dosed supply of an aqueous ammonia solution to prevent hydrolysis of TNBA.

DND can be introduced into the process in the form of a dry substance or in the form of a paste with the appropriate solvent in which the acylation is carried out, or in the form of an aqueous paste. In the latter case, before adding the mother liquor and PNBH, it is necessary to dehydrate the DND. Dehydration is carried out by azeotropic distillation of water with a solvent.

PNBH can be introduced into the process as a solid or as a solution in an appropriate solvent in which acylation is carried out.

Ferric chloride can be introduced into the process in the form of dry anhydrous ferric chloride FeCl ₃ by loading it directly into the acylation reactor or by adding it to the solution of BNP. Ferric chloride can also be introduced into the process in the form of FeCl ₃ · 6H ₂ O crystalline hydrate or as an aqueous solution by adding it to DND followed by dehydration by azeotropic distillation with a solvent.

In accordance with the invention, it was found that during mother liquor recycling, impurities do not accumulate in TNBA in quantities that prevent its further processing into 5 (6) -amino-2- (4-aminophenyl) benzimidazole. This is illustrated by the examples below. The melting point of TNBA obtained using mother liquor recycling did not fall below the required value of at least 194 ° C (see table).

As a result of the process according to the proposed method, the consumption rates of raw materials are reduced, the output of TNBA is close to quantitative, the amount of production waste is reduced, significant savings in energy resources and labor are achieved, environmental pollution is prevented.

The drawing shows the dependence of the degree of DND conversion on time in the acylation reaction of 4-nitrobenzoyl chloride in chlorobenzene at 120 ° C.

The invention is illustrated by the following examples.

Example 1

139.7 g (0.763 g mol) of 2,4-dinitroaniline (DND), 162.8 g (0) are charged into a ³ -necked flask with a capacity of 2 dm ³ equipped with a stirrer, a reflux condenser connected to a hydrogen chloride recovery system and a thermometer. , 8776 g mol) of 4-nitrobenzoyl chloride (PNBH), 0.68 g of anhydrous ferric chloride and 472 cm ^{3 of} chlorobenzene. The excess PNBH is 15 mol.% In relation to the bottom.

The reaction mass is heated with stirring. At a temperature of 85 ° C, intense evolution of hydrogen chloride begins. The mass is heated, gradually increasing the temperature to 134-135 ° C for 1 hour, and holding at this temperature in a boiling mode holds for 2 hours until the completion of the evolution of hydrogen chloride.

Next, the flask is cooled with water, and then in the refrigerator to a temperature of 5-10 ° C and the resulting suspension is filtered on a Buchner funnel with suction using vacuum. The TNBA precipitate was washed with 210 cm ^{3 of} chlorobenzene. The main and wash filtrates are combined. Get 665 cm ³ chlorobenzene mother liquor containing, g / DM ³ : DN 0.71; PNBH 20.0; TNBA 9.87; 4-nitrobenzoic acid (NBC) 2.63; FeCl ₃ 0.50.

Chlorobenzene is distilled off from the TNBA paste with water vapor, the suspension is cooled to 30-40 ° C and neutralized with a 0.25% ammonia solution to pH 8. Aqueous ammonia is added gradually, twice in 50 ml portions and at the final stage of neutralization of 20 ml. In this case, a subsequent portion of aqueous ammonia is added when the ammonia contained in the previous portion reacts. Next, the aqueous suspension of TNBA is filtered off, washed with water to remove the ammonium salt of the NSC. 243.5 g of TNBA are obtained (96% of theory). Melting point 195.8 ° C, content,%: DND 0.1; NSC Ot .; The pH of the aqueous extract is 0.68.

Example 2

In the flask described in example 1, load 665 cm ^{3 of the} mother liquor obtained in example 1, 139.2 g of DND, 149.77 g of PNBH and 0.48 g of FeCl ₃ . The total amount of reagents and the molar excess of PNBH with respect to DND are the same as in Example 1. The reaction mass is gradually heated with stirring. The temperature is gradually increased to 132 ° C over a period of 0.5 hours (boiling of the reaction mass) and held for 2 hours. In the process of exposure, 80 cm ^{3 of} chlorobenzene are distilled off using a direct refrigerator and combining the processes of solvent distillation and acylation. The temperature in the reaction mass rises to 134-135 ° C. Next, the reaction mass is treated as described in example 1. Get 780 cm ³ chlorobenzene mother liquor, having the composition, g / DM ³ ; DNA 0.67; PNBH 18.40; TNBA 10.20; NSC 3.01; FeCl ₃ 0.52. This mother liquor is used in the next recycle operation. The TNBA chlorobenzene paste is placed in 1200 ml of water and chlorobenzene is distilled off in the form of an azeotrope with water. TNBA in an aqueous suspension is neutralized by the metered addition of 280 cm ^{3 of a} 0.25% aqueous ammonia solution at a temperature of 50-35 ° C, adjusting the reaction of the medium to a stable pH value of 8. The neutralized suspension of TNBA is filtered and washed with water. The yield of TNBA 250.8 g (99.0% of theoretical). Melting point 194.6 ° C; content,%: DNA 0.18; NSC Ot .; The pH of the aqueous extract is 6.8.

Example 3

In a three-necked flask with a capacity of 2 dm ³ , equipped with a stirrer, a thermometer, a three-horned nozzle with a dropping funnel, a reflux condenser with a direct refrigerator and a receiver, 154.4 g of DND wet paste containing 139.15 g of the basic substance, 1 g of an aqueous solution of FeCl ₃ are charged, containing 0.48 g of ferric chloride and 300 cm ^{3 of} chlorobenzene.

The contents of the flask are heated with stirring and the water is distilled off in the form of an aeotrope until the start of distillation of anhydrous chlorobenzene. Then the mixture of DND with chlorobenzene in the flask is cooled to 70 ° C with stirring, a reflux condenser is installed in the three-neck nozzle, 758 cm ^{3 of the} chlorobenzene mother liquor obtained in Example 2 and containing 0.5 g DND, 14.0 g PNBCH, 7.7 are charged g of TNBA, 2.3 g of NSC, 0.4 g of FeCl ₃ and 751 cm ^{3 of} chlorobenzene.

The reaction mass is gradually heated with stirring for 1 hour to a boil (132 ° C). Then the reflux condenser is removed and when the reaction mass is boiled and stirred from a dropping funnel for 1.5 hours, 331 g of a 45% solution of PNBH in chlorobenzene containing 148.9 g of PNBH are added. The total excess of PNBH with respect to DND in the synthesis is 15 mol%.

In the process of adding the PNBH solution, 570 cm ^{3 of} chlorobenzene are distilled off through a reflux condenser and a direct refrigerator. Next, the reaction mass is treated, as in example 1. Get 670 cm ³ chlorobenzene mother liquor having the composition, g / DM ³ : DND 0.90; PNBH 17.30; TNBA 13.72; NSC 2.0; FeCl ₃ 0.54. This mother liquor is sent to the next recycling experience. The TNBA chlorobenzene paste is placed in 1200 ml of water, chlorobenzene is distilled off and neutralized with aqueous ammonia. Consumption of 0.25% ammonia water 240 cm ³ . After filtering the aqueous suspension and washing with water, 251.4 g of TNBA are obtained (99.1% of theory). Melting point 194.8 ° C; content, wt.%: DND 0.20; NSC 0.05; The pH of the aqueous extract is 6.9.

Examples 4 and 5 are presented in the table.

Example 6

610 cm ³ mother liquor isolated in example 5, is treated before entering into the synthesis of TNBA activated carbon OU-B. To do this, in a three-necked flask with a capacity of 1 dm ³ , equipped with a stirrer, a direct refrigerator and a thermometer, 140 g of water paste containing 75 g of activated carbon OU-B in terms of 100% are loaded, 255 cm ^{3 of} chlorobenzene are added and 65 ml of water are distilled off in the form of an azeotrope with chlorobenzene until a temperature in pairs of 131 ° C is reached. Next, 610 cm ^{3 of the} mother liquor obtained after synthesis of TNBA in Example 5 is introduced into the flask. The mass is heated with stirring to 80 ° C, kept for 0.5 hours, cooled to room temperature, then the mother liquor is filtered off with coal on a Buchner funnel with suction.

Get 660 cm ³ chlorobenzene mother liquor having a composition, g / DM ³ : DND 0.86; PNBH 17.2; TNBA 7.1; NSC 2.2; FeCl ₃ 0.44. This mother liquor is sent to the next recycle operation. 634 cm ^{3 of} purified mother liquor containing 0.55 g of DND, 10.9 g of PNBH, 4.5 g of TNBA and 1.4 g of NBA are charged into the reaction flask, as in examples 1 and 2. 139.1 g of DND, 151.9 g of PNBH and 0.5 g of ferric chloride are added. The molar excess of PNBH is 15%. Acylation is carried out as described in examples 1 and 2. 180 cc ^of chlorobenzene are distilled off during boiling. TNBA is isolated and neutralized in an aqueous suspension with ammonia at a temperature of 50-30 ° C, gradually adding 300 cm ^{3 of a} 0.25% aqueous ammonia solution to a stable pH of 8. After filtration and washing with water, 248.8 g of TNBA are obtained (98, 2% of theoretical). Melting point 194.4 ° C; content, wt.%: DND 0.12; NSC 0.01; The pH of the aqueous extract is 6.8.

Chlorobenzene mother liquor in a volume of 650 cm ³ containing, g / dm ³ : DND 1.1; PNBH 19.8; NSC 2.2; TNBA 7.8, used in the next synthesis of TNBA.

The table shows additional examples illustrating the proposed method for producing TNBA.

Claims (6)

1. The method of obtaining 2 ', 4,4'-trinitrobenzanilide by acylation of 2,4-dinitroaniline 4-nitrobenzoyl chloride in the presence of a catalyst when heated in an organic solvent, characterized in that the acylation of 4-nitrobenzoyl chloride, taken in excess of more than 5 mol.% By relative to 2,4-dinitroaniline, is carried out with a gradual increase in temperature to a boil at atmospheric pressure in the presence of ferric chloride as a catalyst, 2 ', 4,4'-trinitrobenzanilide is isolated by sequential crystallization, filtration and neutralization of am miakom in an aqueous suspension, the reaction mother liquor formed after crystallization and filtration is returned to recycling for the next acylation operation and neutralization is carried out at a temperature not exceeding 60 ° C with a metered supply of aqueous ammonia. 2. The method according to claim 1, characterized in that the organic solvent used is chlorobenzene, paraxylene, orthoxylene, a technical mixture of xylenes, ethyl benzene or toluene. 3. The method according to claim 1, characterized in that the catalyst used is a crystalline hydrate, or an aqueous solution of ferric chloride, or a crystalline powder of anhydrous ferric chloride. 4. The method according to claim 1, characterized in that the process is carried out with an excess of 4-nitrobenzoyl chloride in relation to 2,4-dinitroaniline 10-15 mol.%. 5. The method according to claim 1, characterized in that the acylation process is combined with the process of distillation of part of the solvent. 6. The method according to claim 1, characterized in that the reaction mother liquor is treated with activated carbon before returning to recycling.

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